Polymers are frequently rendered flame-resistive by adding phosphorus and halogen compounds or mixtures thereof to them. Some polymers are processed at high temperatures, for example at 250.degree. C. or higher. For this reason, many known flame retardants are unsuitable for such applications, since they are too volatile or are not sufficiently heat-resistant.
Alkali metal salts of phosphinic acids are known as flame-retardant additives for polyamide molding materials (DE-A1-2 447 727). However, they tend to exhibit corrosion effects.
It is an object of the present invention to provide flame retardants which do not have the disadvantages of existing flame retardants. For example, the flame retardants shall be simple and inexpensive to prepare and possess good flame retardancy and also high temperature resistance (e.g. resistance to temperatures of at least 250.degree. C.).